Require Go 1.15 or later

The library github.com/golang-jwt/jwt/v4 requires the FillByte() method
of *big.Int, so we're raising the minimum Go version to 1.15.

.github/workflows/tests.yml

@@ -55,12 +55,6 @@ jobs:
             test_fuse: true
             install_verb: get
 
-          - job_name: Linux
-            go: 1.14.x
-            os: ubuntu-latest
-            test_fuse: true
-            install_verb: get
-
     name: ${{ matrix.job_name }} Go ${{ matrix.go }}
     runs-on: ${{ matrix.os }}
 

CONTRIBUTING.md

@@ -66,8 +66,8 @@ Development Environment
 The repository contains the code written for restic in the directories
 `cmd/` and `internal/`.
 
-Restic requires Go version 1.14 or later for compiling. Clone the repo (without
-having `$GOPATH` set) and `cd` into the directory:
+Make sure you have the minimum required Go version installed. Clone the repo
+(without having `$GOPATH` set) and `cd` into the directory:
 
     $ unset GOPATH
     $ git clone https://github.com/restic/restic

changelog/unreleased/pr-3680

@@ -0,0 +1,7 @@
+Change: Update dependencies and require Go 1.15 or newer
+
+We've updated most dependencies. Since some libraries require newer language
+features we're dropping support for Go 1.14 and restic now requires at least Go
+1.15 to build.
+
+https://github.com/restic/restic/issues/3680

doc/020_installation.rst

@@ -274,7 +274,7 @@ From Source
 ***********
 
 restic is written in the Go programming language and you need at least
-Go version 1.14. Building restic may also work with older versions of Go,
+Go version 1.15. Building restic may also work with older versions of Go,
 but that's not supported. See the `Getting
 started <https://golang.org/doc/install>`__ guide of the Go project for
 instructions how to install Go.

go.mod

@@ -51,4 +51,4 @@ require (
 	gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
 )
 
-go 1.14
+go 1.15